[feature request] add support for audio source selection

[Theodor]

Could you add a function to select the sound source so that you can specify whether the sound will be recorded from a computer or from a microphone or from there and from there (I apologize in advance if the function exists and I did not read the manual well)

[Ilia Bozhinov]

It does exist, the -a option supports specifying the audio device to capture from, take a look at issues like #131